1. Field of the Invention
The present invention relates to an illumination device for illuminating the operation panel of electronic instruments installed on vehicles for example, and particularly to an illumination device which can be mounted on a circuit board by being held by suction at the top surface of the cap which is fitted on the light emitting element such as a lamp.
2. Description of the Related Art
FIG. 6 is a cross-sectional view of a conventional illumination device. The illumination device A, which is disposed behind the operation panel (nose section) of a vehicle-installed electronic instrument, is used to illuminate from inside the operation keys and indicators attached and formed on the panel.
Conventional illumination devices of this type have been designed such that lead terminals 4 of a light emitting element 2 such as a lamp are soldered by being led out through a through-hole of a circuit board B. However, the structure that requires the insertion of the lead terminals 4 in the through-hole is not satisfactory in the efficiency of mounting the light emitting element 2 on the circuit board B. On this account, the illumination device A shown in FIG. 6 is provided with a casing 1 for supporting the light emitting element 2, and the casing 1 is mounted flatly on the surface of the circuit board B.
The casing 1 is made of hard resin, with a cavity-shaped holding section 1a being formed at the center. A through-hole 1d is formed in the bottom of holding section 1a of the casing 1. Grooves 1b are formed to run across the bottom and side walls of the casing 1 and merge with the through-hole 1d.
The light emitting element 2 is held in the holding section 1a. Lead terminals 4 of the light emitting element 2 are led out through the through-hole 1d and seated by being bent in the grooves 1b, and have their end sections hooked on the shoulder 1e of the casing 1.
A colored cap 5 is fitted in contact with the side surfaces of the light emitting element 2 and the holding section 1a of the casing 1. The cap 5 is made of soft synthetic resin and colored in a red-like or blue-like color. The cap 5 transmits part of the white light emitted by the light emitting element 2 to create the illumination light of the cap color.
The illumination device A is placed on the circuit board B, with its bottom surface of casing 1 being in contact with lands L of conductor strips formed on the circuit board B, and the lead terminals 4 which are exposed to the exterior of the bottom and side walls of the casing 1 are soldered to the lands L. The soldering work is based on the reflowing process using cream solder (paste solder).
However, although the illumination device A shown in FIG. 6 is designed to be mounted flatly at the bottom surface of casing 1 on the circuit board B, the working efficiency of mounting the casing 1 on the lands L of conductor strips by hand is unsatisfactory.
It is desirable to carry the illumination device A to the position over the lands L of the circuit board B by holding by suction the casing 1 or cap 5 of the device using a vacuum suction nozzle of automatic part mounting equipment used commonly for mounting other parts such as IC devices. The conventional illumination device A shown in FIG. 6, however, has a dome-shaped top section (a) of the cap 5, and therefore it is difficult for the vacuum suction nozzle to hold the dome-shaped top section (a) unless it has a special nozzle shape.
One possible solution is using a vacuum suction nozzle 6 having an inner diameter set approximately equal to the outer diameter of the cap 5 so that it holds by suction the outer surface (b) of the cap 5. However, the presence of a gap between the outer surface of the cap 5 and the inner surface of the nozzle is inevitable, and it is difficult to hold the cap 5 by suction stably.
Another possible solution is using a suction nozzle 7 having a sufficiently large inner diameter so that it holds by suction the upper surface (c) of the casing 1. This scheme provides the more stable suction holding as compared with using the nozzle 6 mentioned above. However, suction nozzle 7 is liable to hit other electronic parts mounted around the illumination device A due to its outer diameter jutting out from the side wall of the casing 1.